Gas recovery



Ma? 31, 1960 w. F. ToMLlNsoN 2,938,927

GAsREcovERY Filed March 27, 195e LMU UnitedStates Patent' Orifice 4 Claims. (Cl. 260-607) This inventionrelates to a method yfor the manufacture of sulfoxides', and more particularly, to an improved process for the manufacture of low molecular weight sulfoxides from the corresponding sulfides. p

United States Letters Patent No. 2,581,050 relates to the vapor phase oxidation of dimethyl sulfide to dimethyl sulfoxide using an oxygen-containing gas which also includes a small amount of an oxygen-transmittin`g nitrogen oxide (such as nitrogen dioxide), yusing reaction temperatures suliicient to maintain the dimethyl sulfide in the vapor phase.

United States Letters Patent No. 2,702,824 relates to e liquid phase oxidation d f sulfides to the corresponding sulfoxides by bubbling a gaseous mixture through the liquid dialkyl sulfide at a reduced `temperature to maintain the dialkyl sulfide in the liqid phase. The gaseous mixture bubbled through the liquid dialkyl sulfide comprises an oxygen-containing gas such as air andv a small amount of an oxygen-transmitting nitrogen oxide such as NO2. d l

In each of the foregoing operations, the temperature control is critical, irl-order to maintain the desired liquid or vapor phase for the reaction, and the catalyst concentration in the oxygen-containing lgas must becarefully controlled. Moreover,` the most practical `oxygen-containing gas` is air which also contains substantialf quantitles of nitrogen. In each of the above described processes, at the end of the process, a substantial quantity of spent gas must beH separated :from the predominantly sulfoxide reaction product. In the above described vapor phase operation, the operating temperature is ordinarily above the boiling point of the sulfide and such spent gases will contain certainquantitiesvofsthe sulfide. 4In the liquid phase process above described, gases bubbling through the liquid phase will tend to carry off substantial quantities of the sulfide (which has.` a relativelywhigh vapor pressure), even though ythe b ody of the sulfide is maintained in the 4liquid phase. Also, substantial quantities of NO will be present in the spentA gases: `If'air is used as the main oxidizing agent, thespont gases `will also contain a very substantial quantity of nitrogen.

. Heretofore, temperature` control was ordinarily employed in an effort to condense out as "rnuh `as possible the sulfide escaping with thegases.A The instant ,invention is based upon the discovery..that sulfide losses in the spent gases can be substantially eliminatedbyscrubbing the spent the sulfoxide obtained inthe reaction which has scrubbed the spent gases theoiigirial reaotionaone. d, t V A i l, ,""It` will also be appreciated that bythe` userofair as the gf gas a continual buildp of nitrogen in "the syste'n'` is a'complisld and such nitrbgen y.must `be ed fromthe Vsysfte'inw4 spent gas. By withdrawing nitrogen frr 'die' system spentgas; evenlf the sulfide has been condensed or bbedyetftf the; spent gas, fesses jef No win als b may befreturned to gases with the A,sulfoxide whi'chmaybe Y, so that the sulfoxide of low molecular Ydialkyl f 'be appreciated, only a smallainount -o'f 2,938,927 Patented May 31, 1960 from the spent gas to any' appreciable extent. The instant invention provides for oxidizing the spent gas so as to oxidize the NO therein to NO2. This is then followed by scrubbing with the sulfoxide, which has `been found to readily remove the NO2 from the spent gas. Throughout the instant specification NO2 is used, al` though it will be appreciated that such NO2 may exist as such or itmay `exist as the polymer N204, both of which function in the same manner hereinand are thus referred to merely as NO2 in `the'instant specification.

It is, therefore, an important object of the instantirr vention to provide an improved method `for oxidizing low molecular weight sulides to the corresponding sulfoxides.

It is a further object of the instant invention to provide an improved method for the manufacture of low molecular weight sulfoxdes from the corresponding sulfides by a process which is made industrially practical by a subsequent scrubbing step which involves scrubbing the spent gases from the reaction with the sulfoxide in order to recover valuable components from the spent gases.

Other objects, features and advantages of the present invention will become apparent to those ski-lledlin the art from the following detailed disclosure thereof and drawings attached hereto and made a part hereo'f.

On the drawings:

Figure l is a flow sheet showing one arrangement for carrying out themethod of the' instant invention; and ,d Figure 2 is a ow sheet showing another arrangement for carrying out the methodV of the instant invention.

As shown on the drawings:

In the assembly generally indicated by the reference numeral 10 in Figure 1,there is provided" a` reaction column 1l 4which may be provided with a filling material or may be Without the filling material packed therein to prevent channelling of upwardly flowingspent gases.y .The sulfide from av suitable sulfide storage tank Siiows into the middle of the column through a line I2. Heating or cooling coils 13 and 14 are provided above and below theV sulfide inlet 12 in` the column 11 for temperature control purposes; An oxdizng'gas such as air (0H-N2) is drawn in through theV intak'e of a blower or compressor 15 and fed into ari inlet header 16 which leads directly into the bottom of the column 1l.- .n oxygentransmitting nitrogen oxide, siich as NGL),l is fed from a suitable storage tnk'into' the inlet header 16 through a line :17. It desired,` air may be blown through the nitrogen oxide storagV container through line 18 (shown as a broken line) and the'n' out through the line 17 intothe header 16.

'Ihe reactions presumably taking place within the column 11 may be represented by the following equatios: (1) S+NO2 S=O+NO wherein 'S is the sulfide S atom and S=O is the sulfoxide grouping. It will be noted that actual'oxidatioh -of the s ulfide to the sulfoxide lis believed to be caused by `reaction'between the sulfide S atom and NO2; Ybut thereslting NO is constantly being regenerated to NO', by'-the presence of the oxygen from'the air. As will th Oxygn- 104 fun 15% U.S. Patent transmitting nitrogen oxide, Asuch as about by volume is employed, according to said No. 2,702,824, and the bulk of the oxidizing gas isoxy'- gen from the air, which is added in an amount just suficient tocomplete the oxidation of the suldei according to saidpatent.l In other words, for `each mol of sulfide one-half mol Vof oxygen is employed (usually with `the twornols 4of nitrogen present inthe air with this amountof oxygen). The resulting `spent gaswhich escapes lfrom the iop of the body of liquid in the column 11 contains a substantial quantity of nitrogen and a relatively smaller quantty of NO, plus sulde and Sulfoxide vapor. The spent gas is essentially a non-oxidizing gas, and it has been found that the amount of Sulfoxide vapor Atherein is extremely minute because of the low vapor pressure of Sulfoxide, but substantial'quantities of sultide are present inthe spent gas. VThe spent gas is separated from the reaction mixture in the column 11v and withdrawn from the top of the column-11 through a conduit 19 into the bottom of a scrubber 20, which is preferably filled with a'llermaterial to give maximum surface area within the scrubber 20 for liquid-gas contact. Sulfoxide is fed into the top of the scrubber 20 from a header 21 and the Sulfoxide removes substantially all of thesuliide from the spent gas in the scrubber 20. More than one scrubber may, ofcourse, vbe used in series in order to completely remove all of the sulfide. Theunique advantage of using the instant sulfv batch.

oxide to remove the sulfide `is that the Sulfoxide has I very great selective solvencyA for the sulfide and it also -has extremely low vapor pressurefat the ordinary operating temperatures (of about room temperature) so that a negligible amount of Sulfoxide will beV carried out of the top of the scrubber 20 in the spent gas conduit 22. A recycle line 23 may beV used, if desired, to return a predetermined portion of the spent gas to the inlet header 16 to be recycled back through the column 11. In this manner, some of the escaping NO in the spent gas is returned toA the system. i

It will be appreciated that, if substantially pure oxygen were fed into the system at the compressor (rather than air) then most of this oxygen, if not all of it, would be consumed in the column 11 and the spent `gases would consist primarily of NO, plus the sulfide. Under such circumstances, substantially all of the spent gases would f he recycled through the recycle line 23 back into the incoming header 16 to be admixed withfresh oxygen. Because of the relatively high cost of substantially pure oxygen, however, it is ordinarily not practicalto use pure oxygen and'air is used. When air is used, it will be vappreciated that nitrogen will build up in the system and all of the spent gas cannot be recycled back through therecycle .line 23. of the spent gas must be released to the atmosphere to prevent the buildup of nitrogen in the gas-cycle. Y In the 4instant arrangement 10, the spent gas to be'purged is -V fed into a reactor 24 where it is admixed with a small amount of air, ordinarily just enough to completely oxidize the relativelysmall proportion of-NO contained in the spent gas. The NO is oxidized to NO2v in the reactor 24, The reactor24, is equipped with adequate coollng coils 2 5 to provide the desiredtemperature for carrying. outf the oxidation reaction therein, so that the NO in the spent gas will be substantially completely Vconverted toV NO2. The .oxidizedY spent 'gas-is: then passed out of-,theV reactor 24; and into: thefbottomof an'- other scrubber 26 through the line 2,1.` Sulfoxide is fed into the top of the scrubber 26 (which may be designed 4 Y tures of the arrangement l10 may also be used with a batch process, wherein a batch reactor is used in place of the column 11 and gas isfcontinuously passed through an inlet header 16 into the bottom of the kettle until substantially all of the sulde in the reactor has been converted to Sulfoxide. The recovery of sulfide from the spent gas in the scrubber 20 can be operated continuously during such batch operation and so also can the recovery of NOz'frorn the spent' gases in the scrubber 26; but this requiresthe use of a somewhat larger batch reactor and -it is preferable to store the Sulfoxide collected in the return .header 28VV forV use in theV next In the continuous arrangement 10 here shown, however, the Sulfoxide is withdrawn from the bottom of the column 11 through the product line 30 and into a rst holding tank 31 equipped with temperature control coils 32, where the Sulfoxide product is warmed slightly. Actually, the Sulfoxide being withdrawn through the product line 30 contains a certain amount of dissolved NO2. The NO2 is readily soluble in the Sulfoxide, whereas the NO is not readily solubletherein. The Sulfoxide may beseparated from the dissolved NO2 in either of two Instead, lan appreciable quantity Y substantially the same as `the scrubber 20 for maximum lliquid-gas contact)V and the Sulfoxide` removes substantially all of the NO2 from the oxi'dized spent gas mix- 'ture ofrNOz andnitrogen, plus' a-slight excess'ofxoxygen, andthe Sulfoxide passes out of the bottom Qthe scrubyber 26 and into the returnhsulfoxide header'28.-which l'also receives SulfoxidefromVthe-,bottom of the ,scrubber ,20 and returns the Sulfoxide from both scrubbers-,20 and 26 1 ntothe column llt'preferably. between the "main suliidelinlet, '12 'and theubottomof .the'c'olunm Nitrogen asses out ofthe top Y.of `'the scrubberZ-through-thepurge outlet 29` to'theatmosphere.- Y :The arrangement 10 of Figure 1 is shwn forfuse with a continuous process wherein the vcrude Sulfoxide 'pr'odlfict Visv continuously withdrawn through a"product 'line 30 leading from the bottom of the column-11.y It will", be

appreciated, however, thatfthe previously describledffa.

ways. VOne way involves merely heating the Sulfoxide in the first holding tank 31 using the heating coil 32 so as to drive out substantially all of the dissolved NO2 which returns to the main inlet header 16 through the line 33 at the top of the holding tank 31. The Sulfoxide is then withdrawn from the bottom of theV rst holding tank 31 through aline 34 into a second holding tank 3'5 also equipped with temperature control coils 36. In the second holding tank 35 the Sulfoxide is cooled down to storage or room temperature and from Ythere it is fed into product storage SO through the line' 37. As previously mentioned, it is preferable to employ the Sulfoxide .pro-- duced in the instant reaction in the scrubbers 20 and 26 and a recycle line 38 recycles the Sulfoxide, or a portion of the Sulfoxide here produced, back to the Sulfoxide header 21 for the scrubbers 20-and 26.

Another way of separating the Sulfoxide from dissolved NO2 which has been found to be practical is to add sul- `tidefrom the sulfide storage S into the irst holding tank 31 in a small amount suicient to react'with all of the NO2 dissolved'in the Sulfoxide. Preferably, a slight'excess of sulfide is fed through the line 39`from the {storage tank S into the holding tank 31 and heating in the tank 31 serves to lremove any unoxidized sulfide as -well as the NO to which all of the dissolved NO2 has been converted. Y

Referring Ynow` toFigure 2- which shows a somewhat different arrangement indicated generallyv by the reference numeral 100, it will be noted vthat the arrangement is made for a process wherein the incoming oxidizing gas consists essentially of NO2. This permits a substantially closed cycle which will be described. VIn thearrangement of Figure 2, sulde `from the sulfide storage S is fed through a line 101 into the middle of a reaction column 102 which is equipped with suitable temperature control coils 103 and V104 above and below Vthe y'sulfide inlet line `101. A gas consisting essentially'ofNOz is fed Vinto the bottom of the-column through theY gas inlet header1(}5f. In the reaction column 102` the NO2 is converted substantially completely to NO and the spent y 'gas' comingorf the top of the body of liquid` in thereactionvcolumn 102 consists mainly of `NO plus sulfide and Sulfoxide vapor. As previously-mentioned, the lou'l vapor'pressure of the Sulfoxide at reaction temperatures causes only a negligible amountrof sulfoxideto be carried over with-the NO, but anjappreciable amount of sulfide t )109, The scrul'nbers10'lA and 109 are iconne'ctedmin series in order to obtain more ccunplete` scrubbing of the NQ. Sulfox'ide is fed from the sulfoxide header 110 into the tops of both of the scrubbers 107 and 109 and ows from the bottom thereof intoa `return sulfoxide heajder ,11-1 which enters the reaction column 102 preferably below the sulfide inlet 101 and above the bottom ofthe column 102.

l y The sulfoxide product takeoff arrangement may be substantially the same as that described in connection with Figure 1. The crude sulfoxide product s withdrawn from the column 102 through the product line 112 and into a first holding tank 113 equipped With suitable ternperature control 'coils 114, wherein the sulforn'de is separated from "dissolved NO2 and/or sulfide; and N0, NO2 and/or sulfide are returned to `the inlet gas header 105 through the line 115. The sulfoxide is then withdrawn from the bottom of the first, holding tank 1,13 'and cooled in the second holding tank 116 with suitable temperature control coils `117 from which it is passed into the product header `-118 which feeds some sulfoxide to the sulfoxide `storage SO and recycles some'sulfoxide through `a line 119 to the sulfoxide header 110 forthe scrubbers' 107 and 109. b b

As indicated, NO2 from the NO2 storagecan be fed -into the incoming gas header 105 and this results in the production of NO which ultimately passes out the top of the second scrubber 109 into -a spent gas header 120 from which the NO is fed linto a reactor 121 equipped with suitable temperature control means`f122t`` 'Oxygen or preferably air is `fed into the reactor 121 through an inlet line 123 in an amount sufficient to convert the NO to NO2 in the reactor 121; This results in a gas mixture of NO2 plus a substantial quantity of nitrogen (if air is used) and `perhaps a slight excess of oxygen which is V'withdrawn through the line 124 from the reactor 121 and fed intothe suction of a compressor 125,l which compressor 125 functions `not only as' thegas pump for Aeffecting continuous ilow of gas in the gas cycle in the'system, 4but which preferably compresses the gas to'super atm`osphericupressure so as to assist in condensing out NO2 from the remainder of the gas. The compressed'gas is fed through the line 126 into a condensing 4chamber 127 equipped with suitable cooling coils 128 wherein the temperature is maintained suf`n`iently low to effect substantially complete condensation of the N05 inthe gas. 'I'he condensing chamber 127 does not require much more than a rather extensive cooling surface, because of the very great 'difference between the boiling points of 15102,l and nitrogen or oxygen which may also be present. The condensed NO2 is then drawn out of the bottom of the condenser 127 into the main lgas inlet 105 to berecycled back into the column V102. Makeup NOZinay be added to the inlet 105 to take care of any losses" which may occur, but the instant'` arrangement is extremely effective in minimizing losses ybecause of the sequence in which the Various process` steps are carried out.

It will also be appreciated that the arrangement 100 canbe modified for a batch process in the mnner', described in connection with the arrangement 10.

vIt will also be appreciated that either the arrangement or the arrangement 100 can b modified so as to be used in a vapor phase oxidation of the sulfide, merely by replacing the column 11 or 102 with a series of gas phase reactors which afford intimate contact between the oxidizing gas and the sulfide at controlled temperatures and which afford means for drawing off sulfoxide product which will condense out at the reaction temperatures. In such cases the return headers 28 and 111 would feed to the crude condensed sulfoxide product. The condensed sulfoxide product will, of course, contain NO and the admixture offsulfoxide containing dissolved sulfide from the scrubbers would result in additional reaction,A so that thet reaction mixture he' yinvolvedwould include not only the gas phase but the liquid condensate phase.

In the practice of the instant invention any of the lower molecular weight sulfoxides may be produced. -Pref'- erably such sulfoxid'es are liquids at ro'om temperature. The corresponding sulfides are preferably fluids (i.`e. gas or liquid) at room temperature and should be iluids at temperatures at least as low as about 10 C., or lower if it =i`s desired to carry out the reaction at a lower tem"n p'erat'ure.

The sulfdes which may be used in the practice of the instant invention include the low molecular weight dialkyl sulfides having the following formula:

wherein each R is the same or a ldifferent C21-5C., alkyl group. vSuch dialkyl sulides include dimethyl sulfide, methyl ethyl sulfide, methyl propyl sulfide, methyl isopropyl suide', methyl n-butyl sulfide, methyl secondary butyl sulfide, etc.; diethyl sulde, ethyl propyl sulfide, etc.; dipropyl sulfideyetc.; and dibutyl sulfide, etc. j The sulfides may also be heterocyclic compounds where S is a nuclear atom. Such compounds include 5 to 6 membered rings having l to 2 nuclear S atoms and the remainder C atoms, in saturated or unsaturated rings, with 1 to 2 substituents on theC atoms, preferably Cl-C; alkyl substituents. Typical types of compoundsare based on the thophene and tetramethylene sulfide'nuclei:

wherein each X is H or a (f1-#C4 `alkyl group but not more than 2 Xs are alkyl groups and the remainder are Hs. Examples include thiophene, tetramethylene sulfide, l-met'hyl tetramethylene sulfide, Z-methyltetramethylene sulfide, 1,3dimethyl tetrarnethylene sulfide, etc. up to 1- butyl tetramethylene sulfide.

b Another heterocyclic compound is based on a 6 membered ringnucleus: `r

wherein Y may ,beS or CXZ and the Xshave fthe meaning hereinbefore given. Examples include pentmethylene sulfide, 1meth`yl pentamethylene sulfide, 2-methyl pentamethylene sulfde, 3-methyl pentamethylene sulfide,A 1,2- dimethyl pentamethylene sulfide, etcfup to the butylpentamethylene sulfides; and dithiane (i.e. diethylene disulfide), 1-methyl dithiane, etc. upto the butyl dithian'es. Members of these groups which are normally solidscan be dissolvedin, for example, dimethyl sulfoxide to provide a liquid composition of the sulfide that is oxidized in the process of the invention. i In the practice of the invention, the organic sulfide may be oxidized in either the liquid or the vapor phase, but in the case of the higher boiling sulfides itis ordinarily preff erable to employ liquid .phase oxidation at lower readily controllable temperatures rather than at higher temperatures requiredV to volatilize the sulfide. In general, sullfides boiling at temperatures above about 7 5 C. should preferably be oxidized in the liquid phase rather than the vapor phase; and sullides which are solids at temperatures above about 75 d C. should `he oxidized in the liquid phase in solution in a sulfoxide such as dimethyl `sulfoxide (or 4any other solvent which is not reactive with the ingrdients liere present, namely, the sulfide, `s`ulfoxde, and NO2). Preferably, the aforementioned temperature f 75 C. should be about 40 Y maximum temperature Vfor carrying out the instant oxidizing reaction. The minimum temperature at which appreciable oxidation takes place is around 10 C. The preferred reaction temperature range is about 2S-40 C.

' contacting the sulfide with The reaction conditions set forth in said United States Letters Patent No. 2,581,050 and No. 2,702,824`may be used in the-practice of the instant invention. lIn addition, a reaction'involving only the sulfide and NO2 may be used, as described generally in connection w'th Figure 2. `In carrying out such reaction the initial step is that of at least a molar equivalent of N05 in the substantial absence of other gases or oxidizing agents, in other words, at least a molar equivalent of a gas consisting essentially of NO2. Since absolute purity of NO2 is not a requirement for the successful operation of the instant invention, it will be appreciated that perhaps l to 15% (by volume) impurities in the NO2 gas can be tolerated, in the form of NO, O2, NZ, etc. The amount of the NO2 introduced into the system in the sulfoxide which is withdrawn from the reaction zone. For 2 molar equivalents of the sulfide. In the liquid phase reaction therev is a tendency for the sulfoxide reaction product to dissolve NO2 and thus retain an appreciable amount of the NO2 introduced into the system in the sulfoxide which is withdrawn `from the reaction zone. For this reason, it is desirable to add a suflicient excessv of 'NO2 to the reaction zone lto permit the loss in NO2 resulting from the withdrawal of the sulfoxide from the reaction zone and also to permit complete oxidation oi the sulfide added tothe reaction zone. Ifvthe NO2` is removedf'rom the sulfoxide reaction product by addition of sulfide thereto, NO will be produced and in the arrangement shown in the drawings the NO will be added directly to the incoming NO2 stream so that the amount of NO in the NO2 stream may sometimes be slightly greater than 10 to 15% by volume. On the other hand, if the dis- Asolved NO2 is removed from the crude sulfoxide product by moderate heating, the NO2 will merely supplement the incoming gas stream; and in either event there'is no material loss of nitrogen oxides. t

It will thus be seen that the instant invention consists in a process for the manufacture of alow molecular weight sulfoxide from the corresponding sulfide by oxidation thereof, which comprises admixing theV Suliide with an oxidizing atmosphere containing an amount of oxygen transmitting nitrogen oxide at least suicient to catalyze the oxidation reaction to produce a reaction mixture containing the sulfoxide and a non-oxidizing spent gas, separating sulfoxide from the other ingredients in the reaction mixture, separating the spent gas from the reaction"v mixture, and' scrubbing the spent gas vwith `sulfoxide and returning such sulfoxide to the reaction mixture. s A As a specific demonstration, in the unit 10 of Figure 1, theoxidation reaction is carried out in the reactor 11 and the'lin'e 19 carries ofi spent gas having the composition: '10% Ydimethyl sulfide, 10% NO and remainder essentially N2.- .(-All percents are by volume.) The spent .gasin the line'l 19r is scrubbed by 0.2 of its volume of dimethyl sulfoxide in the scrubber 20 and the resulting gas in the line 22 has the composition: 10%.NO, 0.5 dimethyl sulfide and remainder essentially N2. The gas in theline 22 is exposed to an equal volume of air to ,oxidizle the NO to NO2 in the reactor 24 and then 'scrubbed in the scrubber, 26 with 0.2 of its volume of dimethyl sulfoxide and the resulting gas composition is .10% dimethyl sulfide, Vtraces of nitrogen oxide and re- ',m'ainder N2 and O2. Y

In the unit 100 of Figure 2, the oxidation reaction is carried out in the reactor 102, using essentially 100% NO2 and the resulting spentr gas inthe line'106 has the composition: %A dimethyl sulfide'and remainder essentially NO. 'The gas in the line 106 is scrubbed with 0.2 volume of dimethyl sulfoxide in the scrubber 107 'and the resulting gas contains only about 0.5% dimethyl LSUIiideLrernainderJNO, kinthe line 108. A second scrub- 8 bing Vin the scrubber 109 reduces the dimethyl sullide to tnace amounts-tin' the line 120); and oxidation by 6 times itsyolume'of air inthereactor 121 converts the NO to NO2 which is removed (all except trace amounts) from the resulting N2 and O2 by compressing to 100 p.s.i. in the pump and cooling to 20 F. in the cooler 127 to liquefy the NO2.` K y It will be understood that modifications and Hvariations may be eected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

l. A process for the manufacturepoffa di-lower alkyl sulfoxide from the corresponding sulfide by oxidation thereof, which comprises admixing the suliide with an oxidizing atmosphere containing Ian amount of oxygen transmitting nitrogen oxide at least sufficient to catalyze the oxidation reaction to produce a reaction mixture containing the sulfoxide and a non-oxidizing spent gas comprising NO 'plus sulde and sulfoxide vapor, separating sulfoxide from the other ingredients in the reaction mixture, separating the spent gas Yfrom the reaction mixture, oxidizing'the'NO in the spent gas to NO2, and scrubbing the spent gas with sul'foxide and returning such sulfoxide to the reaction mixture.

2. A process for the manufacture .of a di-lowerV alkyl sulfoxide Vfrom'the vcorresponding rsulfide by oxidation thereof, whichvoomprises admixing the sulde with an oxidizing atmosphere containing an` amount of voxygen transmitting nitrogen oxide at least sufficientto catalyze the oxidation reaction Y to Aproduce a reaction mixture containing the sulfoxide and -aY non-oxidizing spent gas comprising NO plus sulfideand sulfoxide vapor, separating sulfoxide from the other ingredients in the reaction mixture, separating the spent gas from the reaction mixture, scrubbing the spent gas with sulfoxide and returning such sulfoxide to the reaction mixture, oxidizing the NO in'the spent gas to NO2, and then removing the NO2 from the remainder of the spent gas and returning the lNO2 to the reaction mixture. 'i

3. A process for the manufacture of a. di-lower alkyl sulfoxide from the corresponding sulride by oxidation thereof., which comprises admixing Vthe suliide with an oxidizing atmosphere 'containing an amount of oxygen transmitting nitrogen oxide atleast suliicient t-o catalyze the oxidation reaction to produce a reaction mixture containing Vthe sulfoxide and a non-oxidizingl spent gas comprising NO plus sulfide and sulfoxide vapor, Yseparating sulfoxide fromfthe other ingredients in the reaction-mixture, separating the spent gas. from the reactionmixture, scrubbing the spent gas with sulfoxide and returning such sulfoxide to the reaction mixture, oxidizing the NO in the spent gas to NO2, and then scrubbing such oxidized Aspent gas. withfsulfoxide toV remove the NO2 `and return the NO2 to the reaction mixture.

. 4. A process for the manufacture of adi-lower alkyl .sulfoxide ,rompthe corresponding sulfide lby oxidation thereof, whichcomprises Vadmixing the sulfide with NO2 .in an amount sufficient to oxidize all of the suliide to sulfoxide ,to produce afreaction mixture containing the sulfoxide and a non-oxidizing spent gas comprising NO plus sulfidegand sulfoxide vapor, sepa-rating sulfoxide from the other ingredients in the reaction mixture, separating the spent gas from the reaction mixture, scrub- Vbmg the spent g-as with sulfoxide `andtreturning'such sulfoxide to the reaction mixture, oxidizing the NO'in theV spentgas to NO2, and then removing the NO2 from the remainder of the spent gas and returning the NO2 to the reaction mixture.

References Cited in the file of this patent*Y Y UNITED STATES VPATENTS 2,581,050 smedsiund '4 7 Jan. 1, 19,52 

1. A PROCESS FOR THE MANUFACTURE OF A DI-LOWER ALKYL SULFOXIDE FROM THE CORRESPONDING SULFIDE BY OXIDATION THEREOF, WHICH COMPRISES ADMIXING THE SULFIDE WITH AN OXIDIZING ATMOSPHERE CONTAINING AN AMOUNT OF OXYGEN TRANSMITTING NITROGEN OXIDE AT LEAST SUFFICIENT TO CATALYZE THE OXIDATION REACTION TO PRODUCE A REACTION MIXTURE CON TAINING THE SULFOXIDE AND A NON-OXIDIZING SPENT GAS COMPRISING NO PLUS SULFIDE AND SULFOXIDE VAPOR, SEPARATING SULFOXIDE FROM THE OTHER INGREDIENTS IN THE REACTION MIXTURE, SEPARATING THE SPENT GAS FROM THE REACTION MIXTURE, OXIDIZING THE NO IN THE SPENT GAS TO NO2, AND SCRUBBING THE SPENT GAS WITH SULFOXIDE AND RETURNING SUCH SULFOXIDE TO THE REACTION MIXTURE. 